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New Homes in the 2050 Coastal Flood Zone

In 2012, Hurricane Sandy slammed into New Jersey, producing a major storm surge and damaging or destroying many thousands of homes. Over the years that followed, builders put up new houses and reconstructed damaged ones, in many areas that will be vulnerable to more flooding in the future — even in the absence of a superstorm like Sandy.

The post-Sandy rebuilding was a striking example of a broader pattern. Across the U.S., coastal communities have recently built tens of thousands of houses in areas at risk of chronic future flooding driven by sea level rise from climate change. That has put homeowners, renters, and investors in danger of steep personal and financial losses in the years ahead.

In a new analysis, Climate Central and Zillow isolated the number of new homes in low-lying coastal areas in all 24 coastal states, projecting how many will become exposed to chronic ocean flooding over the coming decades — depending on what choices the world makes around greenhouse-gas pollution today.

New homes in the 2050 coastal flood zone in these states

If the world makes moderate cuts to greenhouse-gas pollution — roughly in line with the Paris agreement on climate — some 10,000 existing homes built after 2009 will be at risk of flooding at least once per year, on average, by 2050. The figures for 2100 are about three times higher under moderate emissions cuts, and five times higher if pollution grows unchecked.

In more than half of U.S. coastal states, the percentage growth rate at which new homes were added inside of America’s highest coastal flood-risk zones outpaced the percentage growth rate outside of those areas. Some communities, in other words, are amplifying their development in flood-prone areas.

New Jersey, North Carolina, Florida, and Texas are projected to see the most new homes at risk by 2050. Between 2009 and 2016 (or 2017 in Florida’s case), those states added a total of roughly 5,700 homes that will lie in the flood-risk zone.

In total, unchecked pollution would put 2.5 million existing homes at risk of yearly flooding or worse by 2100. Those properties are currently worth $1.33 trillion — an amount equal to 6 percent of the U.S. economy. No state has more to lose from such a future than Florida: unchecked pollution would put 730,000 more homes in flood-risk zones than would moderate cuts to emissions — and 960,000 more than deep cuts.

Methodology: “Risk zones” are first classified as areas with elevations below local projected sea levels plus annual flood heights, and refined by removing low-lying areas that appear to be protected from the ocean. Assessment is based on accurate, high-resolution data provided principally by the National Atmospheric and Oceanic Administration. Local sea level projections are based on Kopp et al. 2017, building on projections from the Intergovernmental Panel on Climate Change and emerging research on the potential instability of Antarctic ice sheets (DeConto and Pollard 2016). Annual average flood levels were derived using water level station data through the end of 2015 for 71 stations. Homes whose coordinates lie within or outside of risk zones were counted and their values, estimated by Zillow, were summed. Only homes with known build years were included in calculations of housing growth rate, which was computed as homes built in 2010 or later, divided by homes built in 2009 or earlier. Address and build year data were provided by Zillow through the Zillow Transaction and Assessment Dataset (ZTRAX; more information here). Proprietary Zillow data were provided under strict confidentiality.